To address the issue of improving the surface integrity of superalloy GH4169,ultrasonic peening and thermal exposure tests were conducted on superalloy GH4169 specimens.The specimens were first subjected to ultrasonic peening tests with a penning coverage of 98%~125% and peening intensity of 0.15 A and 0.25 A. Then the specimens were thermally exposed at 250 °C,400 °C and 550 °C for 1 hour and 10 hours respectively. Finally,the effects of ultrasonic peening on the surface roughness,hardness,microstructure and residual compressive stress of superalloy GH4169 were analyzed,as well as the changes in residual compressive stress after thermal exposure. The results indicate that after ultrasonic peening,the surface of superalloy GH4169 undergoes plastic deformation and the surface hardness significantly increases.The grain refinement in the near-surface layer is significant,and the grain size shows a gradient distribution from the surface layer to the depth,introducing residual compressive stress in the surface layer.Compared to 0.15 A,the peening intensity of 0.25 A increases the grain refinement by 29%.After high-temperature thermal exposure,the residual compressive stresses on the surface of superalloy GH4169 undergo thermal relaxation,with the maximum rate occurring at the initial stage of thermal exposure,after which it tends to stabilize and becomes independent of the duration of thermal exposure.The higher the thermal exposure temperature,the more intense the relaxation of the near-surface residual stress and the greater the depth at which the maximum residual compressive stress is located.
图11为试样截面的KAM统计图。基于核心区域的平均取向差(kernel average misorientation,KAM)是表示晶粒晶格畸变特征的主要参数之一,能够反映微观局部塑性变形的均匀化程度,数值较高的地方塑性变形程度较大[21]。通过对比可知,形变位置主要发生在晶界附近,试样塑性变形程度呈梯度分布,由表层至材料内部逐渐减弱,试样S2的塑性变形程度更大,范围更广,这与之前的试验结果一致。
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